The present invention relates to a method for controlling plasma density or its distribution over the target configuration of a magnetron source, a method for the production of coated workpieces, as well as magnetron sources.
Definition
By magnetron source is understood a sputter source, on which the discharge is operated with DC, AC or mixed AC and DC, or with pulsed DC, wherein AC is to be understood as extending up into the HF range. The source is conventionally operated under vacuum with a working gas, such as for example argon, at pressures of a few mbar up to 10xe2x88x923 mbar. In known manner, reactive additional gases can be mixed in for reactive processes.
Over the sputter surface of the target configuration at a magnetron source, a tunnel-form magnetic field is generated, which, in a view onto the surface to be sputtered, the sputter surface, forms a closed loop. Viewed in the cross sectional direction of the target configuration, at least a portion of the magnetic field emerges from the sputter surface and enters back into it again in the form of a tunnel arch. The sputter surface, also referred to as the target surface, forms the one electrode, the cathode, of the plasma discharge gap, since positive ions must be accelerated onto the target surface for the sputtering process. This electrode can also be subdivided and its components can be individually electrically supplied.
Consequently, in the region of the loop of the tunnel-form magnetic field an electric field obtains, which is substantially at an angle with respect to the tunnel field. A tunnel-form electron trap results and a pronounced electron current, which substantially circulates in and along the loop of the tunnel-form magnetic field. In the region of said loop-form circulating magnetic field this electron current produces a pronounced increase of the plasma density compared to the plasma density further outside of said magnetic field loop.
Therewith along the circulating electron current, referred to in the technical field as xe2x80x9crace trackxe2x80x9d a substantially increased sputter rate, results which leads to an increasingly more developed erosion trench in the sputter surface, i.e. at the base of the tunnel-form circulating magnetic field.
Apart from fundamentally the great advantages of magnetron sources, this increasingly developing erosion trench, has negative effects on
Coating homogeneity on the coated substrate,
Degree of utilization of the target material.
In order to avoid at least partially these disadvantages, it is known to move, in particularly cyclically, entire or major portions of the magnetic field circulating tunnel-form in a loop with respect to the target configuration or its sputter surface. Thereby is obtained a temporal distribution of the xe2x80x9crace trackxe2x80x9d electron current effect along the traversed sputter surface regions.
If it is taken into consideration that the looped magnetic field circulating in the form of a tunnel is conventionally realized by a configuration of strong permanent magnets beneath the target configuration, it is evident that, on the one hand, an existent permanent magnet configuration which, for shifting said magnetic field, is mechanically moved beneath the target configuration, can only be geometrically changed with relatively high expenditures, in order to realize different erosion profile distributions, and that in sputter operation a variation of this distribution or of the geometry of the permanent magnetic configuration is hardly possible.
The present invention addresses the problem of being able to control the plasma density or plasma density distribution over the sputter surface of the target configuration differently or additionally and therein also to be able to carry out this control during the coating process.
This is achieved with the method of the above described type thereby that locally, i.e. along a limited partial segment of the circulating loop of the tunnel-form magnetic field, this magnetic field and/or the electric field is varied under control. In a second solution formulation the posed problem is solved thereby that onto the tunnel-form magnetic field basically a controlling magnetic field is superimposed. Under the first formulation, the corresponding field is thus locally varied, under the second an additional magnetic field is superimposed onto the tunnel-form one.
U.S. Pat. No. 5,512,150 discloses a magnetron sputter source, in which the tunnel-form magnetic field over the target configuration can be varied with respect to its radial extension. For this purpose beneath the target configuration an electromagnet is disposed in the form of a pot, whose poles can be reversed by reversing the current direction. This electromagnet itself generates the tunnel-form magnetic field: for that reason, it must be extremely strong, which leads to a large voluminous coil with corresponding heat development.
The disadvantages of this known process according to the invention are circumvented under both formulations.
It was found according to the invention that through the exclusively local change of the electrical and/or of the tunnel-form magnetic field the electron trap is more or less disturbed, which corresponding to the particular operating point and the selected variation, leads to an increase or decrease of the plasma density along the entire electron trap.
With respect to the average periphery of the electron trap therein the described local intervention is realized in a peripheral region, in top view, of maximally ⅓ of the perimeter, preferably on a region of maximally xc2xc of the perimeter, preferably in a region which is significantly shorter.
Relative to the average pole distance d of the pole regions out of which the tunnel-form magnetic field emerges from the sputter surface and enters it again, a preferred length lB of the xe2x80x9clocalxe2x80x9d region on which the intervention is carried out, preferably results as:
0 less than lBxe2x89xa64d
preferably
0 less than lBxe2x89xa62d
in particular of
0 less than lBxe2x89xa6d.
When the term xe2x80x9clocalxe2x80x9d is used, then preferably with the above addressed geometric reference to average loop perimeter and/or to average pole distance, in particular averaged in the considered intervention region.
Even if, under the second formulation of the present invention, onto the tunnel-form magnetic field a controlling magnetic field is superimposed no longer necessarily locally, such that the degree to which the anode intervenes in the resulting magnetic field is varied under control, a controlling effect is exerted onto the action of the electron trap and the circulating electron current and consequently onto the plasma density and sputter rate along the entire circulating loop.
According to the first listed formulation of the present invention in a preferred embodiment the tunnel-form magnetic field and/or the electric field is varied locally with control such that said degree is varied.
Since according to the first formulation of the invention the magnetic field and/or the electric field is only locally intervened upon, it is entirely possible to vary the tunnel-form magnetic field and/or the electric field through the controlling intervention on their particular generators themselves, thus without superposition.
If, according to the second formulation of the invention onto the circulating tunnel-form magnetic field a controlling magnetic field is superimposed, this takes place in a preferred embodiment along at least one major portion of the loop of the tunnel-form magnetic field. The superimposed field is preferably established substantially perpendicularly to the target sputter surface and, in a further preferred embodiment, substantially homogeneously, i.e. with locally constant field strength distribution. But it is entirely possible to develop this superimposed field also locally of different amplitude and/or to vary it such that its controlling strengths differ.
The two formulations, according to the invention, can be entirely realized in combination.
In terms of equivalent circuit diagram, varying the circulating electron current can be considered a variation of the plasma impedance of the particular discharge zone or loop.
If, in source operation, on a target configuration more than one electron trap is provided with the particular magnetic field loop, this can be considered as a parallel circuit of the plasma impedances associated with the tunnel field loops. This leads to a further highly advantageous effect of the present invention: if the control according to the inventionxe2x80x94according to one or according to both stated aspectsxe2x80x94is employed at least with one of the electron traps, this manifests itself as a control of an impedance of an impedance parallel circuit, from which results a control of the current distribution onto the parallel impedances. Consequently, a control and corresponding redistribution of the plasma densities, sputter powers and sputter rates on the provided loops or electron traps takes place. In the case of the at least two electron traps under consideration, one can be disposed within the other, or they can both be adjacent to one another.
Furthermore, in a further preferred embodiment the at least one electron trap with its loop of the tunnel-form magnetic field is moved during operation over the target configuration or its sputter surface, preferably under control and preferably cyclically, be that for example in a pendulum-like or in a continuous circulating movement.
In particular under the first aspectxe2x80x94application of a local controlling changexe2x80x94with the variation the form of the loop of the electron trap is varied under control, preferably cyclically or according to another temporal program, or the electron trapxe2x80x94also under the second aspectxe2x80x94under control, preferably cyclically or according to another temporal program, is attenuated or augmented, up to their switching off or on.
The control according to the invention can take place in discrete steps or continuously. If two of said control variables, magnetic field and electric field, are employed simultaneously, discrete control and continuous control can, if appropriate, be combined.
In a preferred embodiment, in particular according to the first solution formulation of the present invention, for the controlled variation of the magnetic field a controllable electromagnet configuration and/or a permanent magnet configuration, movable under mechanical control, and/or a ferromagnetic shunt configuration is employed, if appropriate, in combination.
If, further, the case is considered of one or several electron traps shifted or moved during operation over the sputter surface, a preferred embodiment is obtained thereby that the controlling electromagnet and/or permanent magnet configuration and/or shunt configuration together with the electron trap(s) is(are) moved. Necessary current supplying can be realized for example via slip rings, in particular under consideration of the low necessary driving powers.
In particular under the second formulation of the present invention, in which not necessarily only locally but preferably over significant regions of the tunnel magnetic field, circulating in the form of a loop, a control magnetic field is superimposed onto it, the superimposed control magnetic field is preferably provided fixed at the source.
The invention relates further to a production method for coated workpieces. Magnetron sputter sources according to the invention are distinguished for the solution of the underlying problem according to other features of the invention and preferred embodiments of the invention. Here also other claimed measures can be employed in combination.
With a sputter coating chamber according to the invention or a vacuum treatment installation as claimed, based on the approach according to the invention highly advantageous vacuum treatments can be carried out, always with the inclusion of the magnetron sputtering according to the invention, wherein substrates result with optimized layer thickness distribution and/or distribution of the layer composition, whose realization until now had only been possible with considerably more expensive procedures.
It should be emphasized at this point that it is understood that the inventive methods, production methods, magnetron sputter sources, vacuum treatment chambers and the vacuum treatment installation according to the invention can also be applied within the framework of reactive coating methods, in which the materials sputtered off the target configuration react with a plasma-activated reactive gas, which is deposited as coating material on the particular substrate(s).
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which a preferred embodiment of the invention is illustrated.